The present invention concerns the surveying of clearances on a railway track to ensure that adequate clearances are maintained for normal traffic and more especially to determine whether sufficient clearance is available for exceptional loads.
It is well known that to avoid contact of any part of a train with obstacles adjacent the track, such as signalling posts, overhead structures, platforms, roofs, bridges, and viaducts, it is important to maintain sufficient clearance to allow for the transverse movements of the train which occur when it is travelling at speed. Such clearances will allow exceptional loads to be transported at low speeds but because the clearances are not uniform in size from one line to another it is often necessary to survey a route in detail before transporting an exceptional load. In the past this has been done by determining the dimensions of the wagon and its load and then measuring the space available at points along the track where it was doubtful whether sufficient clearance existed. Obviously this is a time-consuming method and it is an object of the invention to provide a more convenient method of assessing whether the required clearance is available.